1. Field of the Invention
The present invention relates to methods and systems related to notifying a mobile terminal device when an interworking function to which it is connected by a wireless link changes to a new interworking function.
2. Description of Background Information
Mobile computing generally involves the use of mobile terminal devices such as notebook computers connected to a computer network (e.g., the Internet) via a wireless communication device (e.g., a mobile phone). xe2x80x9cMobile IPxe2x80x9d is a functionality in wireless communications where mobile terminal devices connected to the Internet may send and receive packets addressed with their home network IP (Internet Protocol) address (a static IP address) while their current point of attachment to the Internet (i.e., their current interworking function) changes. This allows the mobile terminal device to maintain its connection with another entity through a packet-based link, and facilitates two-way communication over that link.
FIG. 1 is a block diagram of a simplified network reference model applicable to mobile computing data services, including mobile IP support. The model shows select network entities forming a communications subsystem 10. A mobile terminal device 12 is coupled to a wireless communication device 14, which is in turn connected to a base station/mobile switching center 16 via a wireless interface. The base station/mobile switching center 16 is connected to an interworking function 18. The simplified network reference model is described in the document entitled xe2x80x9cData Service Options for Wideband Spread Spectrum Systems,xe2x80x9d TIA/EIA/IS-707, Published Version (February, 1998), the content of which is hereby expressly incorporated by reference herein in its entirety (herein referred to as xe2x80x9cIS-707xe2x80x9d).
According to IS-707, mobile terminal device 12, communication device 14, base station/mobile switching center 16, and interworking function 18 are respectively referred to as a TE2 device, an MT2 device, a BS/MSC and an IWF. The interface between mobile terminal device 12 and the wireless communication device 14 is called a Rm interface. The interface between wireless communication device 14 and base station/mobile switching center 16 is referred to as an Um interface. The interface between base station/mobile switching center 16 and interworking function 18 is referred to as an L interface.
Mobile terminal device 12 may comprise, for example, a notebook computer, a personal digital assistant, or any other computing device capable of computer network communications, including packet-based communications or communications via a dial-up modem. Wireless communication device 14 may comprise, for example, a wireless terminal used by subscribers to access the network services over a radio link. The wireless terminal may comprise a hand-held cellular telephone, or a unit installed in a vehicle. Wireless communication device 14 may,also be fixed to a particular location.
Base station/mobile switching center 16 is shown in FIG. 1 as a single functional entity, although it need not be. The base station portion of the illustrated base station/mobile switching center allows wireless communication device 14 to access network services using a radio link or another type of wireless link. The mobile switching center portion handles the switching of traffic between the wireless link and a telecommunications network to which the wireless link is connected. The telecommunications network may comprise one or a combination of public switched telephone: network (PSTN), integrated services digital network (ISDN), internet routers, and other network types and entities.
Interworking function 18 represents the point at which a gateway or bridge connection is formed between mobile terminal device 12 and/or wireless communication device 14 at one end and the Internet at the other end.
FIG. 2 is a simplified diagram of a protocol stack adhered to by many mobile computing environments, including those adhering to IS-707. The stack comprises one or more lower layer(s) 28, a data link layer 26, a network layer 24, and one or more upper layers 22. One or more lower layers 28 are provided. These lower layers include, among other things, connections establishing a physical link, and may also include a relay layer as disclosed in IS-707, a paging channel 30, and a traffic channel 32.
Data link layer 26 is immediately above lower layer(s) 28. Data link layer 26 may utilize such protocols as PPP and/or SLIP. This layer deals with point-to-point communication between two computers. It packages addressing data, and manages the flow of transmissions. PPP is described, for example, in RFC 1661, xe2x80x9cThe Point-to-Point Protocol,xe2x80x9d (July 1994), the content of which is hereby expressly incorporated by reference herein in its entirety. PPP facilitates the transmission of datagrams between data communications equipment from different manufactures over a dial-up and dedicated serial point-to-point links. PPP can simultaneously transmit multiple protocols across a single serial link, without the need to set up a separate link for each protocol. PPP also allows the interconnection of dissimilar devices, such as host bridges and routers, over serial links. The PPP protocol is comprised of three main components, including an encapsulation scheme, the link control protocol, and network control protocols. These components are respectively responsible for creating the frame, controlling the link, and managing the network layer protocol.
Network layer 24 is just above data link layer 26, and may comprise such protocols as IP or connectionless network protocol (CLNP). The network layer ensures that information arrives at its intended destination. That is, it is concerned with the actual movement of information from one network entity to another. The internet protocol (IP) breaks up data messages into packets, routes the packets from a sender to a destination network entity, and reassembles the packets into the original data messages at the destination. The IP protocol contains an IP header which contains source and destination address fields that uniquely identify host computers respectively acting as the source and destination of the packets being transferred.
Upper layer(s) portion 22 comprises one or more protocol layers above network layer 24, including, for example, the TCP (transmission control protocol) that facilitates the reliable in-order delivery of an input data stream.
Various protocol techniques are specified to achieve IP mobility support in RFC 2002, xe2x80x9cIP Mobility Support,xe2x80x9d (October, 1996) (hereinafter referred to as xe2x80x9cRFC 2002xe2x80x9d), the content of which is hereby expressly incorporated by reference herein in its entirety. As described in RFC 2002, IP mobility support allows a mobile node to communicate with other nodes after changing its link layer point of attachment to the Internet, yet without changing its IP address. The mobile node will ideally be able to communicate with other nodes that do not implement these mobility functions, and there should be no need for protocol enhancements in hosts, routers, or bridges that are involved in the routing of packets to and from the given mobile node that supports IP mobility.
xe2x80x9cAgent discoveryxe2x80x9d is a method disclosed by RFC 2002 by which a mobile node will determine whether it is currently connected to the Internet via its home network or via a foreign network, and when it is connected through a foreign network, the mobile node detects when it has moved from one foreign network to another. Agent discovery involves both agent advertisements and agent solicitations which can be sent and received by mobile nodes, foreign agents, and home agents. Network entities called xe2x80x9cMobility Agentsxe2x80x9d send agent advertisements which are received by the mobile node and which indicate when a given foreign network changes. These agent advertisements are sent over traffic channel 32 to the mobile node which, in the network model shown in FIG. 1, comprises mobile terminal device 12. However, there are circumstances in which it is desired that a link be maintained between the mobile node (i.e., mobile terminal device 12) and the point of attachment (i.e., interworking function 18) even though traffic channel 32 is down. For example, IS 707.5 sets forth a dormant mode for packet data services, in which the traffic channel is down while the PPP link (within data link layer 26) and the IP link (within network layer 24) extending between the mobile terminal device 12 and interworking function 18 are maintained. Under these circumstances, a mobile terminal device 12 will not receive the agent advertisements alerting it when there is a change in its location from a first geographic region to a second geographic region, requiring that the link be switched to a new/second interworking function.
There is a need for a mechanism to allow mobile terminal device 12 to be timely notified of a change in its interworking function 18, which will occur as a result of wireless communication device 14 moving from a first geographic region to a second geographic region.
3. Definitions of Terms and Acronyms
The following term and acronym definitions are provided to assist the reader in obtaining an understanding of the invention as described herein.
Flow control: An act performed by a receiving entity to limit the amount or rate of data sent to it by a transmitting entity.
Interworking Function (IWF): A point at which a gateway or bridge connection is formed between a given network (e.g., a packet network) and mobile devices coupled to the network by way of a base station and/or a mobile switching center.
In view of the above, the present invention, through one or more of its various aspects and/or embodiments, is thus presented to bring about one or more objects and advantages. One such object is to provide mechanisms and protocols which allow a mobile terminal device to become aware of a change in its point of attachment to a packet network to which it is connected. A further object of the present invention is to provide a mechanism by which the wireless communication device can notify the mobile terminal device of the change in the point of attachment so the mobile terminal device can update its registration of its IP address and continue to enjoy the benefit of IP mobility.
The present invention, therefore, is directed to a system or a method including a mechanism for updating a transmission link over which a mobile packet network call is established when the wireless communication device moves, requiring a change in a given interworking function. The transmission link extends between a mobile terminal device and a given interworking function, and connects the mobile terminal device to a wireless communication device over a first interface. The transmission link further connects the wireless communication device to the given interworking function over a second interface via a wireless link to a base station. The given interworking function changes from a first interworking function associated with a first geographic region to a second interworking function associated with a second geographic region when the wireless communication device moves from the first geographic region to the second geographic region. The transmission link comprises, among other elements, a traffic channel, a data link layer link, and a network layer link. The transmission link comprises a packet mode in which the traffic channel is up and a dormant mode in which the traffic channel is down while the data link layer link and the network layer link are maintained. Network region identifier information is provided to the wireless communication device when the transmission link is in the dormant mode (and also when the traffic channel is up). The wireless communication device determines when the given interworking function has changed from the first interworking function to the second interworking function by determining when there is a corresponding change in the network region identifier information.
The wireless communication device initiates a link control protocol negotiation with the mobile terminal device when the change in the network region identifier information has been determined. The mobile terminal device responds to the initiation of the link control protocol negotiation by sending link control protocol packets to the second interworking function via the wireless communication device. The transmission link then enters the packet mode and brings up the traffic channel. The data link layer link is then established with the second interworking function. After the data link layer link with the second interworking function is established, the mobile terminal device and the second interworking function negotiate network control protocol options and establish a network layer link therebetween. When appropriate, the mobile terminal device updates its mobile IP registration.